Sulphur isotope study of Ni-Fe-Cu mineralization in the Shetland ophiolite

Analysis of 62 samples show that the sulphides throughout the igneous stratigraphy have a magmatic signature, with the exception of the uppermost gabbros and the lowermost basal thrust talc-carbonate lithologies. Mean delta-34S values for whole-rock samples from harzburgites, dunite pods in harzburgite, crustal dunites and wehrlites, the main and high-level pyroxenites and gabbros suggest that the primary sulphides derived their sulphur from a magmatic source enriched in 34S. This finding is compatible with the proposed origin of the ophiolite above a subduction zone. Values for pyrite mineralisation in the uppermost part of the gabbros are thought to result from precipitation from a seawater-derived fluid, while isotopically light sulphur in the basal thrust could have been introduced from underlying metasediments. The replacement of pentlandite by heazlewoodite has not led to sulphur fractionation